1. Field
The present invention relates to a method and apparatus for evaluating a digital information signal and, more particularly, to evaluate the digital signal to ensure that the signal is transmitted error-free.
2. Discussion of Related Art
In the transmission of a digital information signal, it must, as a rule, be expected that the information signal is subject to interference or is overlaid by an interference signal. To extract the digital data from the information signal, the information signal is, as a rule, fed to a comparator as a digitizing device that extracts the data or the individual bits from the information signal. In this process, however, the interference may result in erroneous digitization of the information signal. In particular, two types of interference may endanger the correct transmission of data. On the one hand, there is continuous interference that can reach the comparator and give rise to error bits therein. If a band-pass filter is inserted upstream of the comparator, it is the continuous interference whose frequency range extends over the filter center frequency of the band-pass filter, that is especially troublesome. On the other hand, there is also aperiodic, short intensive interference that may comprise sufficient energy to induce the comparator to respond. Such aperiodic, short interference may also pass through the band-pass filter and likewise result in erroneous data.
A method is disclosed for evaluating an information signal containing digital data, that includes amplifying the information signal with a variable gain. The information signal is then compared with a digitization threshold to extract the digital data. The information signal is also used as an actual value for an integral-action controller having a setpoint value, which is a controller threshold and has a value lower than a value of the digitization threshold. A control signal is then output from the integral-action controller that alters the amplification of the information signal in such a way that the variable gain is continuously increased when the information signal is less than the controller threshold and is continuously reduced when the information signal is greater than the controller threshold.
A circuit arrangement for evaluating an information signal containing digital data is also disclosed. The circuit arrangement includes an amplifier circuit having a variable gain for amplifying the information signal. A comparator circuit is provided for comparing the information signal with a digitization threshold to extract the data. Also included is an integral-action controller having an actual-value input to which the information signal is applied and having a setpoint value that is a controller threshold, the value of which is less than the digitization threshold. The integral-action controller is configured to continuously increase the variable gain of the amplifier circuit when the information signal is below the controller threshold, and to continuously decrease the variable gain when the information signal is greater than the controller threshold.